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PUBLIC HEALTH INTERESTS CONCERNED IN THE PRES- 
ERVATION OF CERTAIN PRIMEVAL FORESTS AND IN 
THE CULTIVATION OF GI^OVES AND TREES. 

Bv FRANKLIN B; HOUGH, M. D.. 

<v - Leivis County, New York. 

A PAPER READ AT THE ANNUAL MEETING IN BALTIMORE, NOVEMBER II,.l875. 

The influence of woodland shade upon the public health, presents a 
theme for thoughtful inquir)', and the more so, because it is almost wholly 
under our control, and as found beneficial, inconvenient, or injurious, it may 
be increased, diminished, or suppressed. We will dismiss from the present 
inquiry all ideas of pecuniary profit or economy, involved in the cultivation 
of timber as a material, or otherwise than in its presumed relations to sani- 
tary science ; and will endeavor to point out the manner in which the culti- 
vation of trees may^ within proper limits, be made a measure of utility as 
regards human health, and the reasons that may be assigned for this influ- 
ence. In doing this, it will be proper to consider as well the direct effects 
of temperature, moisture, electricity, and other physical causes, as the less 
tangible but not less real effects by which, through the senses, they operate 
upon the mind. 

It will be conceded that a country wholly and densely covered with a for- 
est, more especially if the surface be level, the drainage imperfect, and de- 
caying organic matter present, is less healthy than one more exposed to the 
sun and open to the winds. In a region thus densely covered, the soil and 
the stagnant air near the surface, are at all seasons overcharged and often 
saturated with moisture, and the decaying vegetation always present, will, in 
hot climates and seasons, tend oftentimes to malarious diseases of a typhoid, 
and sometimes of a malignant type. These humid conditions, in colder 
regions, and in winter, predispose to pulmonary and rheumatic diseases. 
These effects are more apparent upon the new-comer than upon one long 
resident, so that the immigrant may suffer, where the acclimated would feel 
little or no inconvenience. 

It is well known that the most virulent forms of malaria have been wit- 
nessed in countries where swampy low-lands have been newly-drained and 
cleared, and the decaying vegetation first exposed in hot seasons to the sun 
and the air, in the first attempts to cultivate the soil. Yet, in most cases, 
where the drainage can be made complete, these conditions will wear away, 
as the organic matter in the soil becomes fully decomposed ; and a region 
once noted for insalubrity may become quite free from malarial diseases, 
and even exceptionally healthy. Thus the Genesee country, in Western 
New York, and the lake region of ^tiiIl:hern Ohio, have, by patient waiting 




PRESERVATION OF FORESTS AND CULTIVATION OF TREES. I'J'J 

and persistent industry, fairly outlived the bad name acquired in the days 
of pioneer settlement. Other regions, like the Maremma of Tuscany, by 
dint of long and costly effort, guided by science, have regained their ancient 
prestige for salubrity; while others, like the Campagna of Rome, remain as 
possible fields for re-conquest, but not without heavy expenditures of life 
and treasure ; and others, like thetropical jungles of India and Afr'ica, which 
have remained since the earliest known period the seat of deadly miasms, 
will probably so continue beyond the power of man to overcome, or, if too 
venturesome, to escape. 

It may be deemed a fact established by frequent observation, that belts 
of woodland, intercepting the sweep of winds from the swamps, purify them 
from malarious emanations ; but whether this be from mechanical obstruc- 
tion, or from the absorption of the poisonous etHuvia of the marshes, has 
not been sufficiently proved by scientific observation. 

But aside from this influence of woodlands upon malaria, the ordinary 
conditions of the atmosphere dependent upon the presence or absence of 
forest shade, present the most interesting themes for observation. Among 
the most obvious of these, is a tendency to the equalization of temperature 
throughout the year ; moderating the extremes of heat in summer and of 
cold in winter, as well as the changes between day and night. 

We know that sudden vicissitudes of temperature, or a steady maintenance 
of either heat or cold, in unusual degree, and for a considerable time, 
operate notably as a predisposing cause of disease. A high and sustained 
heat, especially if it continues into the night, as in tropical climates, is de- 
bilitating in its effects. Under this influence, the muscles, and with them 
the heart and arteries, lose their powder and tone. Respiration is reduced in 
frequency, the cutaneous and bilious secretions are increased, and that of 
the kidneys is diminished, the nervous energy is relaxed, and a general lan- 
guor and debility is induced, predisposing to dysenteric and other intestinal 
disorders, and bringing the system to that condition most susceptible to dis- 
eases of a typhoid or adynamic type. It is at such- times, especially when 
putrescent organic matter is allowed to diffuse its emanations near human 
habitations, that malignant epidemics appear and spread, until finally sub- 
dued upon the return of confirmed cold weather. 

A person who has been exposed to unusual heat for a length of time, 
without apparent injury, may suffer sooner from the sudden alterations of 
temperature liable to occur at the close of the hot season ; and hence autum- 
nal fevers, and other* forms of disease, appearing at the end of summer, 
and which are sometimes more fatal than the sickness of midsvmimer, may 
prove more malignant, because the system, weakened by long exposure to 
heat, is then less able to withstand these sudden transitions between heat 
and cold. 

A low temperature, when extreme and long continued, operates as a direct 
sedative ; abstracting the animal heat faster than is consistent with full 
health, and reducing all the vital powers, weakening the circulation, arrest- 
ing or greatly reducing the cutaneous secretion, increasing that of the kid- 
neys, and tending to cause internal congestions and pulmonary disease. 



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1 78 PRESERVA TION OF FORESTS AND CUL TIVA TION OF TREES. 

Excessive moisture, with extremes of cither heat or cohl, may Ije said to 
generally aggravate their injurious tendencies. A very dry air exerts on the 
body the influences due to rapid evaporation and a high degree of electrical 
tension, which, while they may be beneficial to some persons, will in others 
tend to excite cutaneous inflammation, fever, and thirst. Its effect, how- 
ever, if not in extreme degree, and too long continued, is more generally 
beneficial than otherwise. 

Any causes, therefore, that tend to moderate the extremes of heat and 
cold, — rendering our winters warmer, our summers cooler, and the country 
less exposed to sweeping winds, which often bring the noxious exhalations 
of marshes far beyond their otherwise normal reach, — maybe ranked as 
salutary, and worthy of attention. These effects our woodlands and groves 
directly tend to accomplish, in proof of which I invite your attention to the 
following thoughts and facts : — 

The tendency to equalization of temperature between winter and summer, 
and between day and night, has been observed in woodlands, in all ages and 
countries, and is within the personal knowledge of every common observer. 
We seek the shelter of the grove in summer for its refreshing coolness and 
shade. Of the throngs that migrate from our crowded cities on the ap- 
proach of the warm season, the greater part seek a rural retreat. No place 
is so inviting as that which offers opportunities for rambling in woodlands, 
and resting in the shade of trees, and our picnic excursions of a day seek 
nothing else. So it has been in every age and country ; and Pliny, writing 
more than eighteen hundred years ago, thus speaks of trees, as rendered in 
the language of his translator, Holland : — 

" In old time, trees were the very temples of the gods ; and according to 
the ancient manner, the plain and simple peasants of the country, savoring 
still of antiquitie, doe at this day consecrate to one god or another, the 
goodliest and fairest trees that they can meet withall. And verily wee our- 
selves adore not with more reverence and devotion, the stately images of 
the gods within our temples (made though they bee with glittering gold and 
beautifuU yvorie) than the very groves and tufts of trees, wherein wee wor- 
ship the same gods in all religious silence. ' First and foremost, the ancient 
ceremonie of dedicating this and that kind of tree to several gods as proper 
and peculiar unto them, was alwaies observed, and continueth yet to this 
day. For the mightie great Oke called ^sculus, is consecrated to jfupiter ; 
the Lawrell to Apollo; the Olive Tree to Minerva; the Myrtle to Venus ; and 
the Poplar to Hercules. Moreover, it is received and believed generally, 
that the Sylvanes and Faunes, yea, and certain goddesses, are appropriate 
and assigned to woods and forests ; yea, there is attributed unto those 
places a certain divine power and godhead, there to inhabite ; as well as 
unto heaven, the proper seat for other gods." 

This esteem for groves, which in the olden time was fostered by religious 
sentiment, and which has in all ages and countries been favored by the com- 
mon sense of mankind, must have some substantial causes ; and here scien- 
tific observation may guide us in determining the elements. We have not 
yet in this country any series of thermomctric and hygrometric records. 



PRESERVA TION OF FORESTS AND CUL TIVA TION OF TREES. 1 79 

made with direct reference to the influence of forests and woodlands upon 
the cUmate, and the extent to which we may, through their agency, modify 
these conditions. The only series of observations that has hitherto been 
made upon this point, upon a scale sufficient to give absolute and trustwor- 
thy results, is that begun in 1867, under the direction of Dr. Ernst Eber- 
mayer. Professor at the Forest Academy at Aschaffenberg, in Bavaria, and 
at stations for comparative observations established at his suggestion at 
other points in Europe. There are now about six of these in Bavaria, ten 
in Prussia, one in Mecklenburg-Schwerin, three in Alsace-Lorraine, one in 
Bohemia, three in Switzerland, and one or more in France. In a corre- 
spondence which I have had with Dr. Ebermayer, he expresses an earnest 
desire for cooperation in the United States, in order that the laws which 
govern these influences may be fully determined. Accidental circumstances 
may affect local observations ; and in order to arrive at general laws, the 
records should be made in various countries and climates, with instruments 
comparable as to their scale, location, and time of observation, and as 
nearly alike as may be in all the circumstances that may affect their indica- 
tions. 

Of course each station should have two places of observation, and two 
sets of instruments ; one in the open fields, entirely away from the local 
effect of the forest, and the other in the midst of its shelter, and fully 
within its influence. 

The instruments consist of common and self-registering thermometers, 
psychrometers, and means for carefully measuring the rain-fall and evapo- 
ration, direction and force of winds, barometric conditions, and, at some 
stations, the electricity and ozone. The temperature in the woods is taken 
at the level of the tree-tops, and at both places at fiv^e feet above the 
ground ; and below the surface at depths of one half, one, two, three, and 
four feet. The hours of observation are at 9 a. m., and at 5 p. m. The 
elastic force of vapor and percentage of saturation are deduced from the 
wet and dry bulb thermometers, and the amount of rain and snow, and rate 
of evaporation by weight and measure. But one set of records is made of 
barometric pressure, and aspect of sky. Care is of course taken to keep 
out from the immediate influence of particular trees, and to see that the in- 
struments shall give a fair average result of the conditions in which they 
are placed. 

These observations, so far as published, tend to show the following 
facts : — 

1. That the average annual temperature of the atmosphere in the woods 
is one and a half to two degrees Fahrenheit below that of the open fields. 

2. That the average annual temperature at the crowns of the trees is 
about one and an eighth degrees above that found in dense woods at five 
feet from the ground ; and that in the former case the average is a little 
over half a degree (|^) below that of unwooded land, at a point five feet 
above the ground. 

3. That in spring the average temperature in the forest is about 3° 
below that of unwooded land, the difference being relatively less among 
deciduous trees than among pines. 



l8o PRESERVATlOiX OF FORESTS AA'D CUI.TIVATIO.V OF TREES. 

4. That the average temperature in the daytime, in summer, in thick 
woods, is 3.78° below that of unwooded hxnd. 

5. That the temperature of the atmosphere within the woods, in the sum- 
mer season, increased 3.94° from the ground to the tops of the trees. 

6. That in autumn, the difference of temperature at five feet from the 
ground, is scarcely i^°, and, 

7. That in winter the difference almost entirely disappears. 

As a direct result of this difference, there is observed a current of air in 
the daytime, from the surface of the ground in the woods, upward and out- 
ward, the cooler air spreading over the open fields. At night, the conditions 
are changed, and we have currents from the fields to the woods, and thus 
alternately, like the land and sea breeze. In some cases the woods were 
found over 8° cooler by day, and 4^° warmer by night, than the open field. 

The differences of temperature may be ascribed, — 

1. To the obstruction of the sun's rays by the foliage, or the direct effect 
of shade. 

2. To the cooling due to ev^aporation that is constantly going on from 
the leaves in the growing season, whereby much heat becomes latent, and, 

3. To the fact that wood is a slow conductor of heat, so that the body of 
a tree, exposed to the sun, or surrounded by warmer air, slowly absorbs 
heat and does not reach its maximum till late in the afternoon, nor does it 
cool down to the temperature of the chilly night-air till near morning. It 
thus absorbs heat by day, and gives it out by night. 

It does not need an instrument to prove that the snows lie on the surface 
much longer in the shade of forests than in open fields ; nor that the shaded 
soil, especially when covered with a matting of decaying leaves, retains 
moisture, and maintains the supply of water for springs and rivulets, while 
the open field is parched with drouth, and summer brooks diminish and dis- 
appear under the drying effects of the sun and winds. Nor is it a theo- 
retical statement, that the retention of snows in climates where they fall, 
has a tendency to delay the premature blossoming of fruit trees, by temper- 
ing the heat of the early spring, until danger from late spring frosts has 
passed, and thus a fruitful season is secured in localities where, without 
this equalizing influence, it would be often lost ; nor can it be doubted 
but that the moderation of extremes in .temperature, which forest shelter 
secures and maintains, results in great benefit to the farmer, as well in his 
fruit and his grain fields as to his farm stock. 

The Bavarian records show that there is less than sixty-four per cent, of 
evaporation from a given surface of water in the woods than in the fields, 
and this difference is about the same at all seasons. Probably the stag- 
nant condition of the air is partly the cause of this, as in dense woods the 
winds but slightly disturb the surface. A large amount of evaporation is, 
however, going on through the growing season from the leaves, so that the 
relative humidity is greater, while the surface evaporation is less. The dif- 
ference is greater in proportion to elevation, and Professor Ebermayer as- 
sumes that the increase of rain-fall caused by large areas of woodlands, in 
some places, is to be attributed merely to the increase of relative moisture 



PRESER VA TION OF FORESTS AND CUL TIVA TION OF TREES. 1 8 1 

within the forests. It is quite evident th|t a cooler temperature would re- 
quire less cooling in woodlands to bring the atmosphere to the dew point. 

These records show that more ozone exists in higher elevations where 
there is much humidity, and less in the rnidst of a dense forest than in 
adjoining fields. 

It has long been known that plants derive their carbon chiefly from the 
carbonic acid always present in the atmosphere, and that by this vital pro- 
cess in the leaf, the oxygen in combination is released. As carbonic acid 
gas is a product of respiration, combustion^ and fermentation, it might 
accumulate in deleterious excess, but for this compensating analysis in 
plants, by wdiich an element essential to life is supplied. By the laws 
which govern the diffusion of gases, and by the action of the winds, this 
process of amelioration is extended over a wide region, and is felt in the 
distant city, as well as the immediate neighborhood. 

It can scarcely be doubted but that woodlands thus tend to promote the 
public health, and that some benefit may result from parks and belts of 
woodland near the great cities, from this cause. 

Electrical Conditions. — There can be no reasonable doubt but that groves 
and woodlands exercise a notable influence upon the electrical conditions of 
the atmosphere, but it remains to be demonstrated, by future researches, 
as to what effect this may have upon the public health. We know that 
there can be no evaporation, no condensation of vapor, no expansion or 
contraction in any form ; in short, no change of place in nature without a dis- 
turbance of the equilibrium of electrical forces, and that when this is not 
conveyed away by conducting bodies, it will be shown by the electrometer 
and sometimes to our senses. We further know that electricity is dissipated 
by points ; and that an insulated branch of a tree cannot be charged, so as 
to manifest the presence of electricity for many moments after the con- 
nection with the prime conductor is withdrawn. When we consider the mill- 
ions of points raised high in air, bristling from every leaf, and thorn, and 
pubescent fibre, on the foliage of a single tree, we may well believe that the 
general result must favor the rapid equalization of electricity, whenever, 
from any cause, its equilibrium is disturbed. 

A house surrounded by high trees is seldom struck by lightning, and in 
the vine districts of France it has been observed that vineyards are more 
liable to injury from this cause, where the timber has been cut away. If 
it be proved, as maintained by high scientific opinion, that hail-storms are 
of electrical origin, this view of the importance of trees in equalizing atmos- 
pheric and terrestrial electrical perturbations, acquires a double value. 

The agency of woodlands in fixing drifting sands, and in intercepting and 
breaking the force of ocean winds, is obvious, nor can we fail to see therein 
an important relation to the public health, as well as great advantage in an 
agricultural point of view. Still greater benefits are promised in climates 
where the Australian gum trees {Eucalyptus of various species) will thrive, 
if half that is said in their favor proves true. It is claimed, concerning 
them, that when planted in marshy groves, they absorb and evaporate the 
moisture of the soil, so as to serve as a measure of drainage in a notable 



1 82 PRESERVA TION OF FORESTS AND CUL TIVA T/ON OF TREES. 

degree, wliilc the foliage emits a hulsaniie aioma, tending to eounteract 
malarious eflluvia, and to rL-nder the atmosphere salubrious around them. 
It is an unfortunate circumstance that the pAicalyptus grows only to perfec- 
tion in a very warm climate, and that its range with us is limited to the 
southern border of the l^nion, and a part of California. 

The hygienic and curative influence of a pine forest, in the case of persons 
predisposed to phthisis, and in the incipient stages of that disease, has been 
claimed by some, and deserves more careful observation. 

But although we find many benefits to the public from the presence of 
sylvan shade, there is a limit beyond which we should not pass, — a kind of 
golden mean between too little and too much, and no country or people is 
so fortunate as that wherein this due balance is carefully maintained. With 
too much, we have a cool, humid climate; with too little, we have a climate 
liable to alternate extremes of heat and cold, — to unreasonable and exces- 
sive floods and to destructive drouths, with all the adverse effect upon the 
public health and human happiness which these conditions imply. Passing 
rapidly from the side of excess, we have already, in many parts of the coun- 
try, begun to realize the evils presented in the other extreme, and may find 
them much more difficult to overcome. Perhaps nothing short of actual 
want, and the high prices which scarcity is sure to bring, will ever thoroughly 
arouse our people to a realizing sense of the necessity of timber culture, 
and our only hope of its success, then, lies in a sublime faith in that trait in 
the American character, which is sure to be manifested, whenever it appears 
that there is money in it. 

Although we claim many benefits to the public from sylvan shade near 
the large centres of population, there is a limit which we should not pass. 
A house too densely shaded is too dark and too damp for health. Its free 
ventilation is obstructed, and sometimes the larvae of insects and other direct 
annoyances, render trees too near a dwelling little better than nuisances. 
This is eminently true with respect to narrow streets in cities, where sunlight 
and the free circulation of air are more needed than shade. 

Business often requires as much light as possible, and hence a thorough- 
fare of trade, or a seat of manufacture, might be seriously incommoded 
by the shade of trees. But along the wide avenue, upon plats of ground 
reserved for public enjoyment, and in the open grounds of suburbs, inviting 
opportunities are presented for the display of good taste, and for refined 
enjoyment, in the cultivation of trees best suited to the conditions, and of 
greatest service for ornament and shade. 

The municipal authorities in many of our cities have been wisely intrusted 
with the care of shade trees in public streets, so that the owner of the ad- 
jacent ground may not plant or remove whatever tree he pleases ; but under 
the right of eminent domain, the public agents are empowered to control 
these measures for the public good. This imposes upon those intrusted with 
these duties a grave responsibility, which, if realized, will lead to a careful 
study of the principles involved, and, if rightly improved, will result in 
great good. 

With reference to city parks, I cannot too strongly commend the plans 



PRESERVATION OF FORESTS AND CULTIVATION OF TREES. 1 83 

that seek to give the greatest benefit to thg greatest number, and within easy 
reach of the humbler classes, that stand in greatest need of their refreshing 
and refining influences. 

Were the alternative presented between a grand public park, in one mass, 
adorned with all that could charm the eye and cultivate the most refined 
taste, yet from distance or regulation accessible only to the wealthy ; or, 
on the other hand^ a series of small reservations scattered here and there 
within easy reach of the masses of the population, connecting by shaded 
avenues, supplied with fountains and resting-places, and tastefully improved 
with such imitations of wild rustic scenery as opportunities allowed, we 
think the true philanthropist would not for a moment hesitate in the choice 
which should confer the greatest happiness upon the greatest number. If 
we can afford both, very well. If not, then let those having means seek 
their opportunities where they can readily find them, in more distant places 
of fashionable resort, where interest is sure to create attractions for those 
that pay. 

Finally, but not least, I will briefly notice an eft'ect upon the public 
health which may be fairly claimed for groves and trees, in the cheerful and 
tranquilizing influence which they exert upon the mind, more especially 
when worn down by mental labor, or convalescent from sickness ; and this 
simple remedy alone might, if seasonably applied, save the lives of thou- 
sands of infants, who, for the want of the fresh air of the fields and groves, 
are every year dying in the crowded quarters of our great cities. The con- 
tact with nature, in such cases, has often a renovating and restorative power 
of positive value, and which every medical adviser must have witnessed with 
great satisfaction. Permit me to cite a case in point, and with this I will 
leave the subject to your consideration. Over twenty years ago, while en- 
gaged in a historical study, I became interested in tracing the origin and 
condition of a remnant of one of our Indian tribes, — the St. Regis In- 
dians, living on the south bank of the St. Lawrence, on the line of forty-five 
degrees north latitude, partly in the State of New York, but mainly in 
Canada. In 1855 I took an opportunity of personally enumerating the fam- 
ilies living on the American side of the boundary, as a part of the State 
census labors then in my charge, and I found them numbering 413. Ten 
years later (1865) they were enumerated by a man of my own selection, and 
I know he did it well. He found the number 426 — an increase of but 13. 
In the month of June of the present year, I accepted an invitation of our 
State officials for again taking their census, as an opportunity for studying 
the growth of a people who long ago had made me an honorary member of 
their tribe ; and personally, with a guide and interpreter, I visited every fam- 
ily, and carefully enumerated every person. The number was 737, an in- 
crease of 311, or over 73 per cent, in ten years ! There had been no immi- 
gration whatever, and the tables showed these increasing numbers in the 
multitude of children under ten years of age. Here was a study, and the 
solution was not difficult. Some thirty years or more ago, these people had 
been permitted by a State law to lease their lands for twenty-one years ; and 
the privilege was granted to many white persons, who cleared small farms, 



184 rRESERVATION OF FORESTS AND CUI.TIVA'l lOX OE 7REES. 

and made iniproveinents, wliich lliey were oblij^ed to leave wlicn their leases 
expired. The Indians coming into possession had moved out of their 
squalid village, and had become small farmers, with an abundance of farm 
produce for subsistence, and plentj' of pure air. As many children had 
been born before as there had been since, but they had nearly all died. 

This striking argument in favor of pure air and rural life should not be 
lost upon those who would benefit their fellow men. We cannot remove the 
humble poor of our great cities away from the labors by which they earn 
their daily bread, nor plant them upon farms, like the Indians of St. Regis ; 
but we can provide them with sylvan shade and fresh air, within easy reach, 
or means of cheap transit to such places, whenever their wasted energies 
require. More especially is this needed for those of tender age, who pine 
and die in the crowded tenements of our cities from the want of pure air, 
and the invigorating inspiration of rural life. In this direction lies our 
greatest hope of future benefit to our crowded cities, towards which, by the 
imperative demands of business employment, the surplus of our population 
is steadily and increasingly tending, by the law of necessity, as uniform and 
unavoidable as that of gravitation itself ; and which, if we cannot prevent 
we must endeavor to control, or, so far as possible, alleviate. 

Now, the fresh air and rural scenery, to which we should invite the classes 
most needing their invigorating influence, are not to be sought in sunburnt 
fields and naked sands, but in cool groves, enlivened with the song of birds 
that there find a safe resting-place and their subsistence upon the insects 
that harm by their excessive numbers, when not repressed. The wasted 
energies of life are renewed by communion with nature in her wild and rug- 
ged forms, which gain new interest when brought in near contrast with the 
improvements of the city, and scattered here and there near the marts of 
trade and the beaten paths of industry. Let us, then, bring home glimpses 
of nature from the wildwood, to relieve the monotony of city life, if by so 
doing we refresh the weary, and make existence enjoyment, where but for 
this timely provision it might prove a burden. 



LIBRARY OF CONGRESS 

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